Bone is an organic/inorganic composite made from inorganic calcium phosphate (CaP) and organic collagen matrix. The inorganic CaP mainly accounts for the mechanical strength of bone while the organic collagen mainly accounts for the toughness of bone. Due to the presence of inorganic CaP, bone is radio-opaque and can be imaged by X-ray techniques. Bone is a living composite because both the inorganic CaP and collagen are resorbable and can be remodeled (i.e., replaced) by bone cells (osteoblasts, osteoclasts and osteocytes.)
Bone cement is typically based upon an acrylic adhesive made from polymerization of methyl methacrylate (MMA) into poly(methyl methacrylate) (PMMA). Since the 1950s, it has been used to fix joint prosthesis implants within the bone. Many common orthopedic surgical procedures (>1 million per year in the US) such as knee replacement, hip replacement, spinal fusion, and tooth repair require the use of bone cement. However, current commercial bone cements have several drawbacks: (1) PMMA bone cement's relatively poor mechanical properties is one of the factors resulting in implant loosening and failure; and (2) PMMA itself is not a radio-dense material and cannot be imaged by X-ray. The addition of radio-opaque material such as BaSO4 or ZrO2 microparticles (e.g., 10% by weight) in commercial formulations further deteriorates the mechanical properties of bone cement due to relatively weak interfacial bonding (Kuhn K-D, Bone Cements, New York: Springer; 2000. 246-247). In addition, PMMA is non-resorbable and cannot be remodeled by bone cells.
U.S. application Ser. No. 13/568,644 describes the formation of magnetic calcium phosphate particles with diameters in the range of 10 nm to 100 μm, polydispersity in the range of 0.01 to 0.5 and a zeta potential in the range of 1 to 60 mVolts. The particles were preferably formed by co-precipitation of iron oxide and calcium phosphate into particles. The magnetic calcium phosphate particles were utilized to treat, prevent or diagnose a particular disease or condition by administering the magnetic particles to a subject, either alone or included with a selected pharmaceutical formulation. The magnetic particles were capable of being drawn to a specific location by use of magnets, thereby providing the feature of magnetic targeting. In addition, the magnetic particles could be used for imaging and labeling of biological compositions.